The catalytic hydrogenation of polycyclic aromatic hydrocarbon feedstocks is well known. For example, in U.S. Pat. No. 3,012,963, there is disclosed a process for selectively converting polycyclic aromatics present in a lubricating oil to incompletely saturated hydrocarbons having one aromatic ring per molecule by hydrogenating the oil at temperatures in the range of 600.degree. F. to about 800.degree. F. in the presence of a nickel sulfide catalyst.
U.S. Pat. No. 3,719,719 discloses a process for selectively partially hydrogenating a polycyclic aromatic hydrocarbon by contacting the aromatic hydrocarbon with hydrogen in the presence of a catalyst consisting of platinum sulfide. Discrete polycyclic compounds and not mixtures thereof are employed as feeds.
U.S. Pat. No. 3,919,287 discloses the conversion of polycyclic aromatic compounds to cyclic olefins using a ruthenium-containing catalyst promoted with a transition metal dispersed in water or an aqueous acid.
U.S. Pat. No. 4,128,473 discloses hydrotreating carbonaceous liquids which contain aromatic compounds to obtain lower boiling liquids. The hydrogenation is described as being at temperatures in the range of 300.degree. C. to 450.degree. C. in the presence of nickel and other transition metals.
U.S. Pat. No. 4,244,808 discloses the use of a transition metal sulfide catalyst in hydrotreating a hydrocarbon fraction of a thermally cracked feedstock and thereafter removing the polyaromatics from the hydrotreated product.
Hydrocarbon feedstocks containing mixtures of polycyclic aromatic hydrocarbons, such as those that are obtained from petroleum residues, coal liquids and from thermal or catalytic cracking processes, typically contain sulfur and nitrogen compounds. These sulfur and nitrogen compounds must be removed or their concentration significantly lowered prior to hydrotreating the feedstock with noble metal catalysts since these compounds have a tendency to poison such catalysts. Transition metal sulfide catalysts, on the other hand, are are not poisoned by sulfur and nitrogen compounds and therefore are useful in hydrogenating such feedstocks. Unfortunately, hydrogenation with transition metal sulfide catalysts generally must be conducted above about 300.degree. C. for reduction to be achieved, and, at these temperatures, there is no selectivity regarding the types of aromatic compounds that are reduced.